The invention pertains to crab traps and more particularly to the type of trap in which the entry tunnel extends inwardly from the side of the trap and terminates at an inner, constricted opening that is in spaced relation to the top, sides and bottom of the trap enclosure and that is oriented so as to open generally upwardly, in facing relation to the top of the trap enclosure.
Traps having an entry tunnel formed as above have proved more effective in holding the crabs captive, once they have entered the enclosure, than have other, prior entry tunnel configurations. By positioning the constricted opening well above the bottom of the enclosure, the bulk of the crabs are held captive because of their natural tendency to stay at or near the trap bottom. Furthermore, by orienting the constricted opening so that it faces generally upwardly toward the top of the trap, greater vertical spacing is achieved between the edge of the constricted opening at which the bottom portion of the entry tunnel terminates and over which the crabs pass as they enter the trap and thence fall to the bottom of the trap enclosure. The greater vertical spacing enables a large number of crabs to accumulate adjacent the bottom of the enclosure, before they pile up to a height that approaches the level of the constricted opening.
In constructing traps of this type, each box-like trap enclosure is usually made with two inwardly opposed entry tunnels made of netting and shaped to converge inwardly, terminating at inner, constricted openings formed by rigid, rectangular hoops to which the tunnel netting is secured. These hoops are in turn connected together by tensioning cords that draw hoops, and thus inner ends of the entry tunnels, toward each other in a mutually supporting relationship. The netting, hoops and tensioning cords are sized and connected together so that the hoops are drawn toward the center of the enclosure and thus toward each other, the plane of each hoop assumes an inclination relative to the sides of the enclosure such that the opening formed by each hoop faces upwardly toward the top of the trap enclosure.
Although more effective than other types of traps, entry tunnels having the above described configuration are not completely effective in preventing escape of trapped crabs, especially when the trap is filled to near capacity. As the trap fills up, the crabs which initially will stay near the bottom of the trap, begin to crawl onto the netting that forms the sides, top and entry tunnel of the trap. Some of these crabs crawl onto the upper surface of a top portion of the entry tunnel netting (i.e., the surface of the tunnel netting that is inside the enclosure and confronts the top of the enclosure) and thence crawl down into the hoop-reinforced opening and out through the entry tunnel.
The number of crabs which escape in this manner is believed to increase in proportion to the number of crabs held captive within the trap, presumably because the overcrowding of the crabs at the bottom of the trap tends to force ever larger numbers of them to crawl up onto the tunnel netting. The losses may be substantial, particularly when a crab trap is left in the water (referred to as a "soak") for more than the optimum of three to four days. When this happens, the number of trapped crabs may accumulate so as to reach or exceed the capacity of the trap, causing increasing numbers of crabs to escape as described above. Additionally, an excessively long "soak" may allow greater time for the crabs to explore possible escape routes, thereby increasing their chances of finding the above-mentioned escape path via the top portion of the entry tunnel netting. Despite such adverse consequences, it is frequently impossible for the crabber to meet the three to four day optimum "soak" interval because of adverse weather conditions or other unpredictable events which interfere with the crabber's schedule, and thus "soaking" is common.
In other crab trap designs, the escape path through the constricted opening of the entry tunnel is blocked off by one-way, hinged gates that allow crabs to pass into the trap but block their escape. For example, in U.S. Pat. No. 2,760,297 issued to F.E. Buyken, each entry tunnel opening is provided with a plurality of wire guards or gates which are hingedly mounted to the upper perimeter of such opening so as to depend generally downwardly therefrom and thus across the opening. These hinged gates are pushed inwardly and upwardly as the crabs enter the trap, and once in the trap, the gates swing back so as to depend downwardly across the tunnel opening, with the free ends of the gates resting on the lower perimeter of the opening, preventing any escape. While swinging gates of the type used in the trap disclosed in the above-mentioned patent, and in other prior art trap designs, are, when properly functioning, effective in blocking the escape of crabs, they have several serious disadvantages. First, the mere presence of the wire gate, obstructing the inner opening of the entry tunnel is enough to discourage some crabs from passing on into the trap. The crabs have very sensitive feelers which sense the presence of the wire gates and it is believed that at least a significant proportion of the crabs will be deterred from entering the trap because of the apparent obstruction. Secondly, hinged joints, involving relative rotation between the gate and entry tunnel structure, such as disclosed in the above-mentioned patent, are not capable of withstanding the adverse environmental conditions to which crab traps are subjected. For example, corrosion around the hinged joint frequently develops, preventing the gates from swinging freely. Also the gates may jam in either an open position or a closed position (the former rendering the gates useless and the latter preventing the crabs from entering the trap). Furthermore, when the gates and supporting structure are made of metal, the loose metal-to-metal contact at the hinge joints causes electrolysis which, in addition to being one of the causes of the above-mentioned corrosion problem, eats away at the adjacent metal thereby requiring frequent replacement of the gates and supporting structure. The electrolysis is also suspected of producing a sufficient voltage difference between the metal parts at the gated opening to cause the crabs which are sensitive to the voltage to be deterred from entering the trap.
Accordingly, it is an object of the invention to provide an improved gate for the constricted opening of entry tunnels in crab traps of the above-characterized type, in which the gate is effective to block the primary escape route in this type of trap and yet is constructed and arranged so as to permit unimpeded entry of the crabs through the constricted opening of the entry tunnel.
Another object of the invention is to provide such a gate which is durable and capable of a long life of trouble-free operation, under the adverse environmental conditions of which crab traps are subjected.
Another object of the invention is to provide such a gate which can easily retrofitted to existing crab traps having entry tunnels of the above-described type.